What is the hormone primarily responsible for maintaining pregnancy early on?

The hormone primarily responsible for maintaining early pregnancy is progesterone. It plays a crucial role after fertilization by supporting the endometrial lining of the uterus, making it suitable for implantation of the fertilized egg. Progesterone helps to maintain the pregnancy by preventing uterine contractions, which helps in keeping the fetus safely implanted.

While hCG (human chorionic gonadotropin) is vital in early pregnancy as it signals to the corpus luteum to continue producing progesterone until the placenta takes over hormone production, progesterone itself is the key hormone that directly sustains the pregnancy in its initial stages. Its production is critical for the maintenance of the uterine environment and for preventing menstruation during pregnancy.

Estrogen also plays important roles during pregnancy, particularly in preparing the body and supporting fetal development, but it is progesterone that primarily stabilizes the early stages of pregnancy. FSH (follicle-stimulating hormone) is involved in reproductive processes related to ovarian function and is not directly related to maintaining early pregnancy. Thus, while hCG is important for signaling and support, progesterone is the main hormone crucial for maintaining an early pregnancy.